Method for the catalytic dehydrogenation of alkylated aromatic hydrocarbons



United States Patent METHOD FOR THE cATALYTrc DEHYDROGENA- $501; 0F ALKYLATED AROMATIC HYDROCAR- Ichiro Tokumitsu, Kiyoshi Watauabe, Harufusa Sue, and Mitito Hamanaka, Tokuyama-shi, Japan, assignors to glemllfsl Petrochemical Co., Ltd., and Idemitsu Kosan No Drawing. Filed July 23, 1968, Ser. No. 746,744 Claims priority, application Japan, Aug. 3, 1967, 42/ 49,536 Int. Cl. C07c 15/10 US. Cl. 260669 1 Claim ABSTRACT OF THE DISCLOSURE The method comprises the step of catalytically dehydrogenating alkyl aromatic hydrocarbon in the presence of steam. Said dehydrogenation is carried out in multistage reactor zones connected in series wherein the reaction mixtures from each individual zone is combined with fresh alkyl aromatic hydrocarbon and steam prior to entering the next reaction stage.

M01. of alkyl aromatic hydrocarbon consumed Mol. of alkyl aromatic hydrocarbon charged Conversion (percent) X 100 M01. of vinyl aromatic hydrocarbon produced Mol. of alkyl aromatic hydrocarbon consumed Selectivity (percent) X 100 In the prior art, it is well known that a vinyl aromatic hydrocarbon is produced by mixing the vapor of the alkyl aromatic hydrocarbon with superheated steam and then passing the resulted mixture into a dehydrogenation reaction zone which usually is a reaction column packed with a dehydrogenation catalyst. However, the dehydrogenation reaction of alkyl aromatic hydrocarbon is particularly severe endothermic, and so, it is difficult to obtain the conversion of more than 40% in said reaction due to temperature depression. Therefore, there has been pro posed a multi-stage adiabatic reaction process wherein superheated steam is blown into the reaction system at each stage during the dehydrogenation reaction to maintain the reaction temperature or an isothermic reaction process wherein a reaction heat is supplemented to the reaction system from the outside of the reaction vessel. However, these prior art processes inavoidably stiller from serious disadvantages. In the isothermic reaction process using a heat-exchanger type reactor, the selectivity obtained is low due to undesired high reaction pressure which is resulted from the shape of a catalyst layer formed in a thin longitudinal tube. In the adiabatic reaction process including the intermittent addition of superheated steam the selectivity obtained in the initial stage in which the most high conversion is attained become remarkably low in comparison with the selectivity of the single stage adiabatic reaction process using the equal "ice amount of steam, because the molar ratio of steam to alkyl aromatic hydrocarbon in the former is small.

The essential feature of the present invention is to carry out the catalytic dehydrogenation of alkyl aromatic hydrocarbon by using multi-stage reactors connected in series, the reaction mixture produced in each of the reactors being fed with fresh alkyl aromatic hydrocarbon and superheated steam prior to the introduction of said mixture into the next stage reactor.

According to the present invention, it is possible to have the remarkably improved conversion in comparison with that of the single stage adiabatic reaction process. Further, it is also possible to obtain the improved selectivity in comparison with the conventional multi-stage adiabatic reaction process using the same amount of steam feed.

The present invention is not limited in the number of stages of the reaction vessel used. However, a twoto four-stage reaction apparatus is preferable at the commercial view point. Any one of the dehydrogenation catalysts can be used for the dehydrogenation reaction according to the present invention.

In carrying out the present invention, the feed ratio of alkyl aromatic hydrocarbon at individual reaction stage can be determined optionally. If the same feed ratio is employed, the steam amount will become larger at the later stage. In the commercial practice, therefore, it is recommendable to add alkyl aromatic hydrocarbon at such a feed ratio as gradually decreasing in response to the reaction stage.

The following examples describe certain Ways in which the principle of the invention has been applied, but are not to be construed as limiting its scope.

Example 1 Vaporous ethyl benzene heated up to 500 C. and steam superheated to 680 C. are mixed at the ratio of 5 kg./hr.:15 kg./hr. The resulting mixture Whose temperature is 600 C. is fed into the first stage reactor wherein ethyl benzene is brought into contact with a dehydrogenation catalyst (pelletized) at LHSV 0.51, said catalyst being in the form of a fixed bed and consisting of 84% Fe O 3% Cr O 12% KOH and 1% NaOH. Dehydrogenation takes place whereby ethyl benzene is converted into styrene at the conversion of about 35%. The reaction mixture of the first stage reactor is then mixed with 2 kg./hr. of ethyl benzene heated to 500 C. and 20 kg./hr. of steam superheated to 750 C., and then passed into the second stage reactor at LHSV 0.52. The reaction mixture of this second stage reactor is mixed with 1 kg./hr. of ethyl benzene (500 C.) and 13 kg./hr. of superheated steam (750 C.) and then passed into the third stage reactor at LHSV 0.73.

Total conversion is 60% which value has never been obtained in the single stage adiabatic reaction process. The selectivity obtained in the process of this example is 92.2%, which is higher than 90.1%, the latter value being obtainable in a three-stage adiabatic reaction process using the same amount of steam feed at the same conversion.

Example 2 Ethyl benzene vaporized and heated to 500 C. and steam superheated to 650 C. are mixed at the ratio of 1.04 kg./hr.:3.3 kg./hr. The resulting mixture whose temperature now is 603 C. is passed into the first stage reactor, wherein ethyl benzene is brought into contact with the fixed bed of a Girdler G-64 catalyst (manufactured and sold by Chemetron Corporation, U.S.A.) at LHSV 0.339. Dehydrogenation takes place whereby a part of ethyl benzene is converted into styrene. The reac tion mixture of the first stage reactor is added with 1.04

kg./hr. of fresh ethyl benzene (500 C.) and 6.2 kg. of superheated steam (850 C.). The total mixture Which now is at 607 C. is passed onto the second stage reactor so as to have the LHSV value of ethyl benzene of 0.398. The reaction mixture resulting therefrom is added with 1.04 kg, of ethyl benzene (500 C.) and 8.5 kg./hr. of superheated steam (850 C.) and the total mixture the temperature of which now is 615 C. is passed into the third stage reactor so as to have the LHSV value of ethyl benzene of 0.318.

Total conversion and selectivity are 60% and 91.9%, respectively, while selectivity of the conventional threestage adiabatic reaction process using the same amount of steam feed at the same conversion is 90.1%.

What We claim is:

1. A method for the production of vinyl aromatic hydrocarbon which comprises catalytically dehydrogenating individual reaction zones prior to the passing of said mixture into the next reaction stage.

References Cited UNITED STATES PATENTS 2,831,907 4/1958 Mayfield et a1. 260-669 2,851,502 9/1958 Bowman et a1. 260669 3,118,006 1/1964 Lovett et al. 260-669 DELBERT E. GANTZ, Primary Examiner CURTIS R. DAVIS, Assistant Examiner 

